This invention relates to hydraulic and pneumatic devices and more particularly to a fluid operated actuator for operating a mechanism such as a clutch operated cable drum.
Various rotating devices are known in which the device is actuated by axial displacement of a mechanism which surrounds a rotatable shaft that operates the device. One example of such a device, of particular relevance to this invention, is a clutch operated cable drum in which a cable drum, a clutch and an actuator are operably disposed along a rotatable shaft so that operation of the actuator causes the clutch to mechanically couple the cable drum to the shaft for rotation therewith.
In one such device, identified by the tradename "TAG-MASTER" and manufactured by the Morin Manufacturing Company of West Springfield, Massachusetts, a conventional spool-like cable drum and a clutch assembly are mounted on a cylindrical shaft which is coupled to a rotating member such as the power takeoff unit of earth moving or excavation equipment (i.e., a power shovel or crane). The cable drum is mounted on a central bearing which allows the cable drum to rotate about the cylindrical shaft and the clutch assembly, which is mounted to rotate with the cylindrical shaft, is operable to cause the cable drum to rotate with the shaft.
More specifically, the outer periphery of an annular, substantially flat friction plate is mounted to one sidewall of the cable drum such that the friction plate extends radially inward toward the shaft and is substantially parallel and spaced apart from one sidewall of the cable drum. To couple the friction plate and hence the cable drum to the rotating shaft, the clutch assembly includes an inner friction disc mounted for rotation with the shaft and postioned between one surface of the friction plate and the spaced apart endwall of the cable drum and includes an outer friction disc which is positioned along the second surface of the friction plate with the central portion of the outer friction disc forming an annular projection or shoulder which is slidably received within a central recess in the inner friction disc. In this arrangement, an annular, replaceable friction lining is mounted to each surface of the friction plate and the inner and outer friction disc includes smooth annular contact surfaces comensuarate in area with and positioned in juxtaposition with each friction lining.
Three tension screws which pass through openings in circumferentially spaced apart recesses within the outer friction disc are threadably engaged with openings in the inner friction disc. Compression springs surround each of the tension screws to urge the outer friction disc toward the inner friction disc thereby urging both friction discs into contact with the friction linings of the friction plate. Thus, by adjusting the tension screws, the cable drum can be operatively engaged to rotate with the cylindrical shaft. In this respect, the tension screws are not utilized to effectively lock the cable drum to the rotatable shaft, but are utilized to establish an initial cable tension or "cable pull". For example, when such a cable drum is utilized as a "haul-in drum" wherein cable is manually withdrawn from the cable drum so that the cable can be attached to an object that is to be drawn toward the machine upon which the clutch operated cable drum is mounted, the tension screws are adjusted such that the two friction discs exert only a small amount of force on the friction plate. Thus, the friction plate turns rather readily between the friction discs and the cable can be easily withdrawn from the cable drum.
By presetting the tension screws to exert various cable tension, such a clutch operated cable drum is adaptable to other situations. For example, by adjusting the tension screws to provide on the order of ten pounds of cable tension, a cable drum such as the "TAG-MASTER" can be used as a "dipper trip" wherein the cable is utilized to actuate a bucket or clamshell of conventional excavating and material handling equipment. In such an application, the bucket or other device can be maneuvered by the equipment operator for scooping up earth or other materials and the preset cable tension prevents slack in the cable as the bucket or other device is moved about. Further, setting the tension screws to exert a preset cable tension on the order of 40 to 60 pounds permits use of such a clutch operated cable drum as a "tag-line winder" for use in applications such as the control of a clamshell, grapple, magnet or other device that is suspended from a maneuverable boom by a conventional pulley and cable arrangement.
In each of the above-described utilizations of a clutch operated cable drum, it is necessary that the apparatus be operable to more positively engage the cable drum to the rotatable shaft, i.e., to greatly increase the cable tension at which slippage occurs between the friction plate and the two friction discs. In this regard, in the operation of such a device as a haul-in drum, it is necessary to effectively lock the cable drum to the rotatable shaft so that cable can be wound on the drum to move an object toward the apparatus upon which the clutch operated cable drum is mounted. In a similar manner, the cable drum must be more positively engaged with the rotatable shaft in order to trip a clamshell or bucket to cause dumping of material that has been scooped up and must be more positively engaged with the rotatable shaft for casting, twisting or snubbing a clamshell or other device during tag-line operation.
To permit the equipment operator to more positively engage the cable drum with the rotatable shaft whenever such action is desired or necessary, conventional clutch-operated cable drums such as the above-mentioned TAG-MASTER include an actuator mechanism which axially displaces the outer friction disc toward the cable drum so that the inner and outer friction discs are more positively forced against (tightly squeeze) the friction plate. In this regard, the outer friction disc includes an outwardly projecting annular collar which concentrically surrounds the rotatable shaft and provides a bearing surface on which the required axial force can be applied.
In conventional clutch-operated cable drums such as the TAG-MASTER, the axial displacement required to actuate the device is generally supplied by one or more pairs of cam arms which are located adjacent the outer friction disc and extend outwardly from the end of the rotatable shaft. The portion of each pair of cam arms that surrounds the rotatable shaft is arranged such that the rotatable shaft freely turns therein and thrust washers, generally formed of brass, are positioned between the outermost cam arm and a jam nut or adjusting collar that is threadably engaged with the end of the rotatable shaft and between the innermost cam arm and the annular projection of the radially displacable outer friction disc. A pneumatic or hydraulic piston, mounted between the outer ends of each pair of cam arms is operable to cause the outer ends of the cam arms to be forced apart from one another and the contacting surfaces of the cam arms are contoured such that the thrust washers are urged outwardly along the rotatable shaft as the cam arms are forced apart. Since the outer thrust washer bears against the adjusting collar, the inner thrust washer moves inwardly to axially displace the outer friction disc and thereby cause the inner and outer friction discs to more firmly grip the lining of the friction plate. Thus, by operating a pair of cam arms, the required increase in cable tension is achieved.
Although the overall operation of such a prior art arrangement is generally satisfactory, the complex arrangement of the cam-like actuator mechanism presents several disadvantages and drawbacks. First, the adjusting collar must be carefully adjusted such that the rotatable shaft can freely turn within the cam arms while being simultaneously adjusted such that operation of the pneumatic or hydraulic piston causes the necessary amount of axial displacement. Further, since the thrust washers are subjected to substantial wear, periodic adjustment is required. In addition, to minimize wear of the thrust washers, lubrication of the thrust washers and cam arms is required as often as every four hours of operation. Even further, the cam arm arrangement is not only expensive to manufacture, but improper adjustment of the adjusting collar often occurs and, as a result, the linings of the friction plate are subjected to additional wear and tear.
Accordingly, it is an object of this invention to provide an improved clutch-operated cable drum which includes an actuator mechanism that does not require adjustment or lubrication with every few hours of operation.
It is another object of this invention to provide a fluid operated actuator mechanism for a clutch-operated cable drum or similar device which is relatively simple in structure and economical to manufacture.
Still further, it is an object of this invention to provide a fluid operated actuator for a clutch-operated cable drum which provides the necessary axial displacement of the clutch mechanism without periodic adjustment and without subjecting the clutch lining to undue wear.